Preparation of unsaturated fluorocompounds

ABSTRACT

UNSATURATED FLUOROCOMPOUNDS ARE PRODUCED BY A COMBINATION OF STEPS COMPRISING (A) REACTING A PERHALOETHYLENE WITH AN UNSATURATED COMPOUND TO PRODUCE A CORRSPONDING CYCLOBUTANE DERIVATIVE TO OBTAIN THE CORRESPONDING PERFLUOROCYCLOBUTANE DERIVATIVE, (C) PYROLYZING SAID PERFLUOROCYCLOBUTANE DERIVATIVE TO FORM THE UNSATURATED PERFLUOROCOMPOUND AND SAID STARTING PERHALOETHYLENE, AND (D) RECYCLING AT LEAST A PORTION OF SAID PERHALOETHYLENE FORMED IN SAID STEP (C) TO SAID STEP (A).

May 9, 1972 w. M. HuTcHlNsoN 3,552,009

PREPARATION OF UNSATURATED FLUOROCOMPOUNDS Filed Nov. 24, 1969 A TTORNE'VS United States Patent O 3,662,009 PREPARATION OF UNSATURATEDFLUOROCOMPOUNDS William M. Hutchinson, Bartlesville, Okla., assgnor toPhillips Petroleum Company Filed Nov. 24, 1969, Ser. No. 879,101 Int.Cl. C07c 21/18, 43/28 U.S. Cl. 260--653.3 9 Claims ABSTRACT F THEDISCLOSURE Unsaturated fluorocompounds are produced by a cornbination ofsteps comprising (a) reacting a perhaloethylene with an unsaturatedcompound to produce a corresponding cyclobutane derivative, (b)fluorinating said cyclobutane derivative to obtain the correspondingperiluorocyclobutane derivative, (c) pyrolyzing saidperiluorocyclobutane derivative to form the unsaturatedperfluorocompound and said starting perhaloethylene, and (d) recyclingat least a portion of said perhaloethylene formed in said step (c) tosaid step (a).

This invention relates to the preparation of unsaturated uorocompounds.In one aspect this invention relates to the preparation oftetrauoroethylene.

For convenience, tetrauoroethylene will sometimes be referred tohereinafter as TFE. Tetrailuoroethylene is an unsaturated fluorocarbonhaving valuable Iutility in various applications. One particularlyvaluable utility is in the form of its various polymers, several ofwhich have achieved commercial success. For example, the polymer orresin Teon is widely used as a coating material in many applicationswhere a coating material having release properties is desired, e.g., inthe coating of cooking utensils. Teon also has other Well-knownutilities. Tetrafiuoroethylene would find even wider application if moreefcient and economical methods of producing same were available. Forexample, tetrauoroethylene cannot be prepared by the direct uorinationof ethylene because a saturated compound is obtained. With ethylene ineconomic and plentiful supply, it would be desirable to have a processfor the production of tetrafiuoroethylene from ethylene.

The present invention provides a solution to the above problems. Thepresent invention provides a process for the preparation oftetrafluoroethylene or other unsaturated fluorocompounds from ethylene,other olefins, or other unsaturated compounds such as tluoroolens,acetylene, or unsaturated ethers. Broadly speaking, the process of thepresent invention comprises an integrated unitary process which,considered as a Whole, comprises a combination of four steps. Said foursteps cooperate to produce the desired product, i.e.,tetrafluoroethylene, by an efficient method not previously known.

An object of this invention is to provide an eflicient process for theproduction of unsaturated fluorocompounds. Another object of thisinvention is to provide an efficient process for the production oftetrafluoroethylene from ethylene. Still another object of thisinvention is to provide an efficient process for the production oftetrailuoroethylene by an efficient combination of steps where-3,662,009 Patented May 9, 1972 ice in tetrailuoroethylene itself is oneof the starting reactants. Other aspects, objects, and advantages of theinvention will be apparent to those skilled in the art in view of thisdisclosure.

Thus, according to the invention, there is provided a process for theproduction of an unsaturated fluorocompound, which process comprises, incombination, the steps of: (a) reacting a perhaloethylene having theformula CF2=CX2 with an unsaturated feedstock compound selected from thegroup consisting of and mixtures thereof, wherein each X is fluorine orchlorine, each Y is hydrogen or fluorine, and Z is CY3-, C2Y5-, CY3O-,or C2Y5O-, and wherein when said unsaturated feedstock compound is aZ-CHICYZ compound the perhaloethylene is tetrafluoroethylene, to producea corresponding cyclobutane derivative having a formula selected fromthe group wherein each Y, each X, and Z is as defined above; (b)fluorinating said cyclobutane derivative to form a perhalo compoundhaving the formula wherein each X is fluorine or chlorine; and Zf isCF3, C2F5-, CF3O-, or C2'F5O-; (c) pyrolyzing said perhalo compoundformed in step (b) to form an unsaturated tluorocompound and saidstarting perhaloethylene of step (a); and (d) recovering saidunsaturated fluorocompound product formed in step (c) and startingperhaloethylene formed in step (c) and recycling at least a portion ofsaid recovered starting perhaloethylene formed in step (c) to said step`(a).

Perhaloethylenes which can be used in step (a) of the combination ofsteps of the invention, include tetrailuoroethylene,chlorotriuoroethylene, and dichlorodifluoroethylene. Unsaturatedcompounds which can be reacted with said perhaloethylene in said step(a) include ethylene, propylene, fluoroethylene, 1,1-difluoroethylene,acetylene, butene-l, methylvinyl ether, 2,2-difluoroethylvinyl ether,ethylvinyl ether, and the like, and mixtures thereof.

iFor purposes of convenience, and not by way of limitation, theinvention will now be further described with particular reference tousing tetrauoroethylene and ethylene as the starting reactants in saidstep (a). IEthylene, being economically available in large quantities,is a preferred starting material. Tetrauoroethylene, being the productof the process of the invention, is thus also readily available. It isan important feature of the present invention that it produces one ofits own starting materials.

'Step (a) in the combination of steps of the invention comprisescyclodimerizing a perhaloethylene, e.g., tetralluoroethylene, with anunsaturated compound, e.g., ethylene, to form a correspondingcyclobutane derivative, e.g., 1,1,2,Z-tetraiiuorocyclobutane. Saidcyclodimerization can be carried out at a temperature within the rangeof from to 600, preferably 300 to 450, C. Generally speaking, fewer sidereactions are involved when the operation is carried out within thepreferred temperature range. Pressures within the range of from 0.5atmosphere to 5000 p.s.i.g. can be employed. Pressures above atmosphericpressure are preferred. Fewer side reactions are obtained at the higherpressures. Said reactants are preferably reacted in a mol ratio ofunsaturated compound to perhaloethylene within the range of from 0.3:1to 50:1, more preferably within the range of from :1 to 20:1. Thesemixtures tend to be explosive and good temperature control is desirable.It is also preferred to carry out the reaction in small diameter tubularreactors. Turbulent flow conditions through the tubular reactors arepreferred so as to promote heat transfer. It is sometimes desirable todilute the reactants of step (a) with a perhalocyclobutane, produced instep (b) to moderate the reaction of step (a).

Step (b) in the combination of steps of the invention comprisesfluorinating the cyclobutane derivative obtained in step (a), e.g.,tetraifluorocyclobutane when tetrafluoroethylene and ethylene are thes-tarting materials in said step (a), to obtain a perhalocyclobutanecompound. Preferably, said -fluorination is carried outelectrochemically by the method of Fox and Ruehlen disclosed incopending application Ser. No. 683,089, filed Nov. 2, 1967, now U.S.Pat. 3,511,760, issued May 12, 1970. Briefly, said process comprisespassing the feedstock to be uorinated into the pores of a porous anode,e.g., porous carbon, disposed in a current-conducting, essentiallyanhydrous hydrogen uoride electrolyte such as KF'2HF. Said feedstockcontacts the fluorinating species within the pores of the anode and istherein at least partially uorinated. Generally speaking, saidfluorination can be carried out at temperatures within the range of from8O to 500 C. at which the vapor pressure of the electrolyte is notexcessive. A preferred temperature range is from about 60 to 105 C.Pressures substantially above or below atmospheric can be employed ifdesired. Generally speaking, the process is conveniently carried out atsubstantially atmospheric pressures. The feedstock to be fluorinated ispreferably introduced into the pores of the anode at a rate such thatthere is established a pressure balance within the pores of the anodebetween the feedstock entering the pores and electrolyte attempting toenter said pores from another and opposing direction. Said feedstockflow rate can be within the range of from 3 to 600 milliliters perminute per square centimeter of anode cross-sectional area, takenperpendicular to the direction of flow and expressed in terms of gaseousvolume calculated at standard conditions. Current densities employed canbe within the range of 30 to 1000, preferably 50 to 5001, milliamps persquare centimeter of anode geometric surface area. Typical voltagesemployed can range from 4 to 12 volts. Converted and unconvertedproducts are withdrawn from the pores of the anode and the productsrecovered from a cell effluent stream. Further details regarding saidFox and Ruehlen process can be Afound in said Pat. 3,511,760.

Said Fox and Ruehlen electrochemical fluorinaton process is thepreferred diuorination process to be used in the practice of theinvention. However, it is within the scope of the invention to employother fluorination processes. For example, direct iiuorination processesusing elemental :fluorine or indirect processes using cobalt trifluoridecan be utilized.

Step (c) in the combination of steps of the invention comprisespyrolyzing the perhalocyclobutane derivative, e.g., octauorocyclobutane,obtained in step (b), to obtain tetrailluoroethylene and the startingperhaloethylene of step (a). Generally speaking, said pyrolysis ispreferably carried out at a temperature within the range of from about1200 to about 1600 F. The conversion level can be maintained within therange of 0.1 to 60 percent; in most instances, preferably within therange of 0.5 to 50 percent. A conversion level of from about 8 to about37 percent has been found to be practical. The pressures employed willpreferably be substantially atmospheric, eg., 0.05 to 5 atmospheres, itusually being preferred to operate at about 1 atmosphere pressure at thereactor outlet. -It is within the scope of the invention to obtaineffective pressures of less than 1 atmosphere by employing vacuum ordiluting the octauorocyclobutane feedstock, eg., with an inert gas suchas nitrogen, so as to lower the partial pressure of saidoctafluorocyclobutane. The contact time can vary over a relatively widerange of values within the range of 0.001 to 2 seconds, or longer,preferably from 0.01 to 1.5 seconds. Usually, the contact time will bewithin the range of 0.05 to 1 second. At any given conversion level andat any given reaction temperature level, there will be a contact timewhich should be employed. However, said contact time is not controllingin that it is fixed, depending upon the conversion level andtemperature. In copending application Ser. No. 873,- 433, filed Nov. 3,1969, in the names of Bjornson and Fox, there is disclosed a definiterelationship between the conversion level and the temperature levelwhich should be observed in order to achieve high selectivity to theproduction of tetrailuoroethylene in the pyrolysis reaction withsubstantially complete elimination of hexaliuoropropene production. IForexample, at a given conversion level there is a reaction tempera-turewhich should not be exceeded. Stated conversely, when operating at agiven reaction temperature, there is a maximum conversion level whichshould not be exceeded. This relationship can be expressed by theformula conversion0.l42t- 166 In the above formula, conversion ofoctauorocyclobutane is expressed in percent, and t is the reactiontemperature in degrees F. Practically speaking, it is usually preferredto employ a tubular furnace, x the temperature at a desired level, andthen control the degree of conversion by varying the rate of flow oftl.e reactant feedstock to said furnace.

Generally speaking, it is preferred that the pyrolysis reaction becarried out in tubular furnaces constructed of any suitable material.The various stainless steels, and particularly stainless steel-Type 304,have been found to be preferred materials of construction for thereaction tubes in the furnace. Inconel is another preferred material forthe construction of the furnace reaction tubes. The furnace tubes arepreferably constructed to have a large surface to volume ratio, e.g., assmall a diameter as practical, so as to promote effective and uniformheat transfer at the generally preferred short contact time. Anysuitable heting means can be employed for heating the reaction tu es.

Step (d) in the combination of steps of the invention comprisesrecycling to step (a) at least a portion of the starting perhaloethyleneformed in pyrolysis step (c), eg., tetrafluoroethylene whentetrafluoroethylene is said starting perhaloethylene. Whentetrafluoroethylene is the starting perhaloethylene, the amount of saidrecycle will be that required to maintain the desired reactant ratio instep (a). When said starting perhaloethylene in step (a) is other thantetrafluoroethylene, all of the perhaloethylene formed in step (c) isusually recycled to step (a). lIn this instance, the amount of the otherreactant in step (a) can be varied to maintain the desired ratio betweensaid reactants. Optionally, make-up perhaloethylene can be added to step(a) as required.

The stream of perhaloethylene formed in step (c) and recycled, at leastin part, from step (c) to step (a), is referred to herein as anessential recycle stream. It is this recycle step which makes theproduction of tetrauoroethylene from ethylene and other similarfeedstocks possible. As mentioned, the iluorination of ethylene orsimilar feedstocks directly results in the production of saturatedcompounds. Because ether linkages are quite stable under uorinationconditions, little or no losses are experienced by cleavage of theethers. The cyclodimerization of the feedstock compound with the recycleperhaloethylene, e.g., tetraluoroethylene, protects the double bond(actually the potential double bond of the tetrafluoroethylene product)from fluorination in step (b) and makes possible the-production oftetrauoroethylene where otherwise a saturated compound would beproduced.

There is real and effective cooperation between each of the steps'of thecombination of steps of the invention. Step (a) produces the startingmaterial for step (b), said step (b) produces the `starting material forstep (c), and step (c) provides one of the reactants .for step (a).Thus, there is real and effective cooperation between the recycle step(d) in that it effectively links all the steps together and completesthe combination of steps of the invention which provides the unique andefiicient method of preparing unsaturated uorocompounds such astetr'auoroethylene from simple and easily available materials,

The drawing is a diagrammatic flow sheet illustrating severalembodiments of the invention.

Referring to said drawing, in one illustrative embodiment of theinvention a stream of ethylene is introduced via conduit into reactor12. Said reactor 12 can be any suitable type of reactor. One presentlypreferred type of reactor comprises a tube and shell heat exchanger withthe reactants being passed through nickel lined tubes, and a suitableheat exchange medium being passed on the shell side in concurrent flowwith the reactants. A recycle stream of tetralluoroethylene, obtained asdescribed hereinafter, is introduced via conduit 14. Said reactor isoperated at a temperature of about 430 C., a pressure of about 4atmospheres, and a residence time of about 90 seconds. In

said reactor 12, stepv (a) ofthe combination of steps of u the inventionis carried out to form 1,1,2,2tetrafluoro cyclobutane by thecyclodimerization of ethylene and tetrauoroethylene, as the principalproduct. A small amount of octafluorocyclobutane is also formed byhomodimerization of tetrafluoroethylene.

Elliuent from reactor 12 is passed through cooler 18 and into separator20 wherein a -iiash separation is effected to remove unreacted ethylenefor recycle' via conduits 22 and 16 to reactor 12. Reactor eflluent,essentially ethylene free, is withdrawn from separator 20 via conduit 24and passed into distillation column 26. A stream comprising thehomodimer, octafluorocyclobutane, is withdrawn overhead from column 26via conduit 28 and passed via conduits 30 and 31 to the pyrolysis step(c) described hereinafter. A stream comprising the codimer,tetrafiuorocyclobutane, is withdrawn as bottom product yfrom column 26via conduit 32 and passed into distillation column 34. A small amount ofheavy products is withdrawn from column 34 via conduit 36. Said codimer,tetrafluorocyclobutane, is withdrawn from column 34 asi`V an overheadproduct via conduit 38 and passed via conduit 40 into electrochemicaluorination cell 42.

Said electrochemical uorination cell 42 can comprise any suitable typeof electrolytic cell having a porous carbon anode and a suitablecathode, e.g., a nickel screen, disposed in a KF-ZHF electrolyte. Ifdesired, the cell container can be the cathode. Make-up hydrogenfluoride is introduced into cell 42 via conduit 44. lFeedstock fromconduit 38, preferably together with a recycle of partially fluorinatedfeedstock in conduit 58, is introduced via conduit 40 into the pores ofthe porous carbon anode at-the lower end portion thereof, travelsupwardly through said anode within said pores and is withdrawn from thepores at the upper end portion of the anode. Within said pores, thefluorination feedstock contacts the fluorinating specles and at least aportion thereof is fluorinated to octauorocyclobutane. If desired, thecell can be divided into an anode compartment and a cathode compartment1n known manner to keep the anode products and the cathode productsseparated. Or, if desired, said cell can be provided with capped anodesto keep the anode products and cathode products separated. However, inmany instances, the anode products and cathode products can be withdrawnfrom the cell together. In the specific embodiment of the invention hereillustrated, the electrochemical uorination cell is operated at anaverage electrolyte temperature of about 106 C., a voltage of about 8volts per cell, a current density of 186 amp/ft.2 and at 0.588 Faradayper hydrogen equivalent per pass, to obtainabout a 15 percent conversionof the total hydrogen in the tetrafluorocyclobutane-containingfeedstock.

A cell effluent stream comprising octalluorocyclobutane is withdrawnfrom cell 42 via conduit 46 and passed into purification zone 48. Saidpurification zonev 48 can be any suitable means for separating hydrogenfluoride and hydrogen from the cell eflluent. For example, absorptiontowers lfilled with sodium uoride in pelleted form can be used to absorbHF from the cell eluent stream. rlwo towers canbe operated alternately,one on process and one on regeneration. Said towers will operate atabout 100 C. on absorption, and can be regenerated on a desorption cycleat about 300 C. -with a countercurrent flowing stream of hydrogen. Therecovered hydrogen uoride is recycled to cell 42 via conduit 50.Hydrogen removed from the cell effluent stream is withdrawn via conduit51.

The purified cell effluent stream is withdrawn from puriiiication zone48 via conduit 52 and passed into distillation column j 54. A bottomstream comprising partially fluorinated products from cell 42 iswithdrawn via conduit 56 and vrecycled via conduit 58 to said cell 42for further ttluorination. A small bleed stream is withdrawn via conduit60 to column 62 for removal of heavy ends from the recycle stream andthus lkeep said heavy ends from building up in concentration in saidrecycle stream.' Said heavyends 'arewithdrawn from column 62 via conduit64. The overhead from column 62 is returned via conduit 66 to therecycle stream in conduit 58.

The overhead stream from column 54 comprising octafluorocyclobutane iswithdrawn via conduit 68 and passed via conduits 30, 31 and 70 intopyrolysis reactor 72 which can be any suitable type of reactor.Preferably, said pyrolysis reactor 72 is a tubular reactor with thereactant flowing through small diameter tubes which can be heated in anysuitable manner, e.g., a liquid metal heat exchange medium, or bycombustion of a fuel, etc. In the specific embodiment of the inventionhere illustrated, said pyrolysis reactor 72 is operated at a temperatureof 1570" F., a conversion level of about 30 percent, and a contact timeof 0.036 second.

Efuent from reactor 72 is passed through cooler 74 and into distillationcolumn 76. A bottoms stream comprising unconverted octafluorocyclobutaneand normal peruorobutane is withdrawn from column 76 viav conduit 78 forrecycle via conduit 80, having check valve 82 therein, to reactor 72.Heater 84 is provided for heating said rec'ycle stream. If desired, saidheater 84 and cooler 74 can be combined in one heat exchanger. A smallbleed stream is withdrawn from conduit 78 via conduit 86 and passed intocolumn 88. The bottoms product withdrawn from column 88 via conduit 90comprises crude normal perfluorobutane and also contains someperuoroisobutylene. Overhead from column 88 is passed via conduits '91and 99 into said recycle stream in conduit to pyrolysis reactor 72.

The overhead stream from column 93 consists essentially of the productand recycle tetrauoroethylene. A portion of said overhead is passed intoconduit 14 for .recycle to reactor 12 and the remainder is withdrawn viaconduit'95 as product. The bottoms stream from column 93 compriseshexauoropropene. Said bottoms product is passed via conduit 96 to column97 for recovery of said hexafluoroprene as overhead therefrom viaconduit 98.

Y The bottoms product from said column 97 is recycled via conduits, 99,80 and 70 to pyrolysis reactor 72.

The principal stream quantities for the above-described specificillustrative embodiments of the invention are set forth in Table I.

TABLE I.CONVERSION OF ETHYENE TO TETRAFLUOROETHYLENE Mols per hour 1Includes about 0.1% of a free radical inhibitor, eg., alpha-pinene,which is removed with heavy products via conduit 36.

While the above illustrative embodiment of the invention starting withother pairs of reactants in step (a), and tion has been set forth interms of starting with tetracontinuing through the drawing substantiallyas described iluoroethylene and ethylene as the reactants in step (a),above in connection with Example I. Thus, the stream the invention isnot so limited. The following Table II 25 numbers in Table II, givenbelow, refer to the streams in summarizes other illustrative embodimentsof the inventhe drawing.

TABLE II Example II III IV V Principal reactants, intermediates,

and products:

Process feedstock CHn=CFi CH=CH CHFCH, CH3CH2CH=CH2n Recyclableperhaloethylene. CF2=CF2 CF=CF CF2=CC1F CF2=CF Cyclodimer H Fa Fri-*- FgH Hg H 02H5 Hg F. F H- u F F c1 F Fg Fluorinated cyclodimer F F2 F F, FF, F

03F 5 1 Fg F Fn F F3 F. F Cl I :Fg- F1 Pyrolyse products lff Sl? Seite,1F";%}"=01"' Step (a) eyclodimer formation:

Temp., C. 350 300 300 250 Press., atm.. 4 50 50 Time, minutes... 20 16612 6.6 Stream 10, mOIS/hr 1 8 o C I 1 10' 01'g2f Stream 14, mols/hr. lr1.0 C2H4 1.0 CgF; 1.0 CzClF; 1.0 CBF; Stream 29, mols/hr 0 5.0 c-C4F 0 0giocifiim gig 001%Et131r 1'i glib 1,11 24 z a 0. z`4 Smm 22 mds/1 0.5c-Ctrs 7.0 com 0.2 cy-cms 0.1 comm Stream, mls/hf z 's 911. ffl Stop (b)electrochemical uorination:

Temp., C 105 98 95 100 Faradays/H equiv./pass .7 0.5 0.6 0.5 Streamames/hf .:fi` 'ifflf P;'if Szt'zgg;

0.15 c-C4Fs 0.15 c-C4Fg Stream 68, molshirm. 0.40 c-C4ClF1 0.54 o-C'Fu20 0C4C12F| Stream 64, niels/hr. 0.11 Step (c), pyrolysis:

Temp., C 800 Press., atm. 1 Tlme, sec.. 0.03 Conversion, percent 20Stream 94, mols/llr-. 1. CgFi 0 2F; 1.0 CEF; Stream 95, mols/hr-. 0.C2F4- 0 zFi. 0 Stream 98, mols/h1 0. CF 1 zClFa 0.01 CaFq Stream 90,mols/hr 0.01 n-CiFm 0 0 0.50 n-C4F5.

e Feed contains 0.15 mol CZIL/mol 04H5.

b Includes about 0.1% of a free radical inhibitor, ag., alpha pinene,which is removed with heavy products via conduit 36. Removed with H2804wash before pyrolysls in step (e).

d 0.05 C12 is added prior to fluorination to maintain level of recycleCFV-:C CIF.

r Product of process.

f Is recycled to step (a) via conduit 14.

The above-described specific illustrative embodiments of the invention,and the data given in Tables I and II, demonstrate the real andeffective cooperation between the steps in the combination of steps ofthe invention.

An outstanding advantage of the process of the invention afforded bysaid cooperation is the purity of the product unsaturatediiuorocompound, e.g., tetrafluoroethylene. This increased purity ispossible in the process of the invention because essentially nohydrogen-containing species or materials are introduced into thepyrolysis reactor in step (c), and hence no hydrogen-containing speciesor materials can appear in said product. Such species or materials are asource of considerable diiculty in conventional prior art processesbecause they act as polymerization chain transfer agents and lower themolecular weight of the polymer when said product is utilized inpolymerization processes. The only impurities present in thetetrafluoroethylene product of the invention are small amounts ofperuoropropene and periluorocyclobutane. These can be reduced to lessthan 100 parts per million by weight by conventional distillation.

While certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifications of the invention will be apparent to those skilledin the art in view of this disclosure. Such modications are Within thespirit and scope of the disclosure.

I claim:

1. A process for the production of an unsaturated uorocompound, whichprocess comprises, in combination, the steps of:

(a) reacting, at a temperature within the range of from about 150 toabout 600 C., a perhaloethylene having the formula CF2=CX2 with anunsaturated feedstock compound selected from the group consisting ofCHZICYZ, CHECH, and Z-CH=CY2 and mixtures thereof, wherein each X istluorine, each Y is hydrogen or uorine, and Z is CY3-, C2Y5-, CY3O-, orC2Y5O-, and wherein when said unsaturated feedstock compound is acompound the perhaloethylene is tetrailuoroethylene, to produce acorresponding cyclobutane derivative having a formula selected from thegroup wherein each Y, each X, and Z is as dened above;

(b) electrochemically uorinating said cyclobutane derivative to form aperhalo compound having the formula 10 wherein each X is tluorine 0rchlorine, and Z, is C173, C2F5, CF3O O1' (c) pyrolyzing, at atemperature within the range of from about 1200 to about l600 F., saidperhalo compound formed in step (b) to form an unsaturated uorocompoundhaving the formula CF2=CF2 or Z-CF=CF2 and said starting perhaloethyleneCFFCXZ of step (a); and

(d) recovering said unsaturated lluorocompound product formed in step(c) and starting perhaloethylene formed in step (c) and recycling atleast a portion of said recovered starting perhaloethylene formed instep (c) to said step (a).

2. A process according to claim 1 wherein said perhaloethylene istetrafluoroethylene.

3. A process according to claim 1 wherein said unsaturated `feedstockcompound is ethylene.

4. A process according to claim 2 wherein said unsaturated feedstockcompouud is 1,1-diuoroethylene.

5. A process according to claim 2 wherein said unsaturated feedstockcompound is acetylene.

6. A process according to claim 2 wherein said unsaturated feedstockcompound is butene-l.

7. A process according to claim 3 wherein said perhaloethylene isl,1,2-triuoro-2-chloroethylene.

8. A process for the production of tetrauoroethylene,

which process comprises, in combination, the steps of:

(a) reacting, at a temperature within the range of from about to about600 C., tetrauoroethylene with ethylene to produce1,1,2,Z-tetrauorocyclobutane;

(b) electrochemically uorinating 1,1,2,2tetrauoro cyclobutane from step(a) to produce octafluorocyclobutane;

(c) pyrolyzing, at a temperature within the range of from about 1200 toabout 1600 F., octauorocyclobutane from step (b) to producetetrafluoroethylene; and

(d) recovering said tetrauoroethylene from step (c) as product of theprocess and recycling a portion thereof to said step (a).

9. A process according to claim 8 wherein in step (d) said recoveredperhaloethylene recycled to step (a) is a major portion of theperhaloethylene reactant used in said step (a).

References Cited UNITED STATES PATENTS 2,462,345 2/ 1949 Barrick260--648 F 2,733,278 1/1965 Anderson 260--653.3 3,306,940 2/ 1967Halliwell 260653.3

OTHER REFERENCES Hudlicky: The Chemistry of Organic Fluorine Cornpounds,pp. 130, 131, 257 and 274 (1962).

DANIEL D. HORWITZ, Primary Examiner U.S. Cl. XR.

260-611'R, 614 F, 648 F UNITED STATES PATMT OFFICE CERTIFICATE OFCORRECTION Patent Nm 3,662,009 Date May 9, 1972 William M. Hutchinson Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Columns 9 and lO, top of page, patent number "2,662,009 should read3,662,009 column 9, line 39, after "fluorne" insert or chlorine Signedand sealed this 5th day of September 1972.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attestng Officer Commissioner ofPatents

